1. Field of the Invention
This invention relates to an angular velocity sensor (or an angular rate sensor), and more particularly to a vibrating gyro type angular velocity sensor suitable for controlling the movement of arms of a robot or suitably used in a navigation system mounted on a car or the like.
2. Description of the Related Art
Most of the conventional angular velocity sensors are incorporated into navigation systems and used in a relatively narrow field of ships, aircraft and the like. With a navigation system, the current position can be determined by integrating outputs of an angular velocity sensor and an acceleration sensor to derive an azimuth and a traveling distance. Since the output error of the angular velocity sensor is accumulated, the error, however small it may be, accumulates to significant proportions; therefore, it has long been required that an angular velocity sensor be developed to have high precision. In recent years, in order to widely supply the angular velocity sensor in the field of a navigation system mounted on a car, a control device for controlling the movement of arms of a robot, and the like, there has been a strong requirement that the angular velocity sensor be lightweight, compact, cheap and easy to handle in addition to high precision.
Gyros have been used in the angular velocity sensor, and various other types of gyro like sensors have been developed based on various principles, but vibrating gyros and forked gyros have received much attention because of their high sensitivity. The vibrating gyros is disclosed in U.S. Pat. No. 5,014,554, for example.
The vibrating gyro utilizes a phenomenon that a Coriolis force acts on a vibrating body in a direction perpendicular to the vibrating direction when a rotation angular velocity is given to the vibrating body. As the vibrating object, a piezoelectric vibrator having driving piezoelectric elements bonded together (bimorph structure) and attached thereto is generally used. The piezoelectric vibrator vibrates in a preset direction when a cyclic voltage is applied to the piezoelectric elements. The displacement of the vibrator in a direction perpendicular to the vibrating direction is detected by a sensing piezoelectric element and output as an angular velocity signal. The angular velocity sensor using the above vibrating gyro has various advantages, but at the same time, it is difficult to form a highly precise angular velocity sensor at a low cost because of variations in the temperature and hysteresis characteristics of the driving and sensing piezoelectric elements, and the state in which they are attached to the vibrator.